The number of internal combustion engines is growing in which alternative fuels or a mixture of fuels can be used. The advantages of such arrangements are discussed, for example, in DE-A-2544444 and U.S. Pat. No. 4,495,930.
In DE-A-2544444 use is made of the fact that an alcohol/petrol mixture has an electrical conductivity which varies in dependence on the ratio of the constituents. The fuel/air ratio required for optimal operation also varies with the fuel constituents and so the opening time of the fuel supply means is varied in dependence on the conductivity measurement. A disadvantage of this arrangement is that an extra component i.e. a sensor is required to measure the conductivity; this adds weight and expense.